Hydrogen peroxide is a widely used oxidant. Although concentrated solutions of hydrogen peroxide are stable, diluted hydrogen peroxide solutions with even trace levels of impurities present tend to degrade significantly during storage or use. Possible causes of the degradation include exposure to heat and radiation, contact with various types of container surfaces and interaction with catalytically active contaminants of the solutions such as transition metals. In particular, the presence of trace amounts of impurities such as iron, copper and other heavy metals can render the solutions unstable resulting in the decomposition of the hydrogen peroxide into water and oxygen during storage or use.
Because of the instability of diluted solutions of hydrogen peroxide, it is desirable to stabilize the hydrogen peroxide to be resistant to in situ oxidation and to form solutions stable toward dilution. It is further desirable for the stabilizer to be effective under acidic conditions.
A number of inhibitors are commonly used in an attempt to stabilize hydrogen peroxide against decomposition. Although organic inhibitors such as acetanilide may be used, they are subject to oxidation by the hydrogen peroxide where hydrogen peroxide is present in high concentrations, thereby significantly reducing the stabilization effect over time.
Tin compounds have long been known as effective stabilizers for hydrogen peroxide. Typical tin compound stabilizers are alkali-metal stannates, such as sodium stannate, which form a tin (IV) oxide sol dissolved in H2O2. The sol is usually co-stabilized by a peptizing agent such as a phosphate or phosphoric acid. Many other organic and inorganic acids are known to be effective co-stabilizers. Among these are benzoic acid, sulfuric acid, nitric acid, sulphonic acids, sulphamic acids, ethylenediaminetetraacetic acid, lactic acid, citric acid and the like.
Tin compounds such as sodium stannate have known toxicity effects. It is desirable, therefore to provide compounds for the stabilization of hydrogen peroxide which are not tin based.
Phosphomolybdic acid (PMA) has been described as a stabilizer for certain organic peroxide compositions in U.S. Pat. No. 5,719,304. However, in hydrogen peroxide solutions, PMA has previously been reported as a catalyst for hydrogen peroxide reactions. U.S. Pat. No. 4,952,712, for example, discloses the use of PMA as a catalyst in the reaction of hydrogen peroxide with a trimethoxytoluene. U.S. Pat. No. 5,030,767 discloses the use of PMA as a catalyst in the reaction of hydrogen peroxide with a substituted phenol. The use of heteropolyacids containing molybdenum as a catalyst for reactions involving hydrogen peroxide has also been disclosed in U.S. Pat. No. 5,608,089. In view of this catalytic action, it would not have been expected that PMA could be an effective stabilizer of hydrogen peroxide solutions.
All US patents and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
It has been discovered that phosphomolybdic acid (PMA) and closely related compounds may be used as a stabilizer for hydrogen peroxide solutions. In addition to PMA, partial alkali salts of PMA can be used to decrease the rate of decomposition of hydrogen peroxide.
One aspect of the invention is a hydrogen peroxide composition including a quantity of PMA compounds effective to retard the rate of decomposition of the hydrogen peroxide component. Another aspect of the invention is a method of stabilizing aqueous hydrogen peroxide by adding an effective amount of a PMA compound to the aqueous hydrogen peroxide to stabilize the hydrogen peroxide against decomposition.
Compositions of the invention may be more reactive for oxidation reactions than non-stabilized H2O2. Use of stabilized compositions of the invention in such reactions is a further aspect of the invention.
While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.
The present invention relates to compositions containing aqueous hydrogen peroxide and phosphomolybdic acid, and/or partial alkali salts of phosphomolybdic acid to retard the rate of decomposition of the aqueous hydrogen peroxide.
Phosphomolybdic acid is a term which refers to any of several acidic compounds of phosphorus, molybdenum, oxygen and hydrogen. Without intending to be bound by any particular molecular structure or mode of synthesis, phosphomolybdic acid can be depicted by the formulas H3PMomOx or H3PO4xtMoO3xdMoO2 wherein m (which equals (t+d)) is typically 10 to 20 but may be higher than 20 or less than 10, and x is typically 34 to 65 but may be higher than 65 or less than 34, and d may be zero. Preferred phosphomolybdic acid for use in the present invention includes compounds corresponding to the formulas H3PMo12O40(CAS Registry Nos. 12026-57-2 and 51429-74-4, also known by P2O5x20MoO3xxM2O); H3PMo12O39(CAS Registry No. 99570-13-5); H3PMo12O38(CAS Registry No. 99559-64-5); and H3PMo10O34(CAS Registry No. 12519-76-5). Other phosphomolybdic acids corresponding to these formulas are also contemplated within the present invention. Phosphomolybdic acid is usually associated with up to about 60 moles of water of hydration per mole of phosphomolybdic acid.
Partial alkali salts of PMA include PMA in which some of the protons are substituted with lithium, sodium, potassium, rubidium or cesium and can be depicted by the formula H3yMyPMonOx where 0 less than y less than 3, M=Li, Na, K, Rb, Cs and combinations thereof, n is 10 to 20, and x is defined above. Desirably 0 less than yxe2x89xa62.5. Stabilized compositions may be prepared by either dissolving solid PMA in aqueous hydrogen peroxide or by combining corresponding aqueous solutions of PIVA and hydrogen peroxide.
In addition to PMA, partial alkali salts of PMA may be used to stabilize solutions of hydrogen peroxide.
Desirably, the concentration of PMA and/or partial alkali salt of PMA in aqueous hydrogen peroxide solution will range from about 0.1 to about 2000 mg/L. More desirably, the concentration will range from about 1 to about 500 mg/L. Most desirably, the concentration will range from about 5 to about 50 mg/L. The exact amount of PMA and/or partial alkali salt of PMA to add will vary and depend on the purity of the aqueous hydrogen peroxide, and on the conditions to which the hydrogen peroxide will be exposed.
The composition may also contain other additives which are stable in the presence of hydrogen peroxide including nitric acid and phthalic acid. Conventional stabilizers, as are known in the art, may also be present.